Screen space 3D diff: a fast and reliable method for real-time 3D differencing on the web

We introduce Screen Space 3D Diff, an interactive method for fast and reliable visual differencing on the web. This method is based on the properties of 3D scenes in 2D space such as depth, color, normals, UV, texture, etc. The central idea states that if two objects project into the same screen space with identical properties, they can be assumed to be identical; otherwise, they are different. In comparison to previous works that require large computational overheads in 3D space, our approach is significantly easier to implement and faster to determine disparities. This is because screen space methods scale with resolution and not scene complexity. They also lend themselves to massive parallelization on modern GPU hardware, and have the added advantage of being accurate at pixel level regardless of magnification. The combination of these benefits allows for instant real-time differencing with minimal disruption to the rendering pipeline even on web browsers. We demonstrate two different implementations of this method; one in a desktop application and one in Unity 3D game engine on the web. The performance of the proposed method across a range of devices is presented and practical benefits of our approach are further evaluated in a user study of twenty professionals with several large-scale models that are typical of the Building Information Modelling paradigm. Based on this evaluation we conclude that our method is invaluable in day-to-day engineering workflows and is well suited to its purpose.